No one "knows what they were getting into."  There are always surprises.  I highly doubt that there is a woman alive who married a man with children who marched down the aisle knowing that they would be unhappy.   I would bet my house that, even when there were red flags waiving furiously in a gale-force wind, there was the belief that with enough love and patience the problems could be overcome.  Every single one of us had the hope of a happy blended family - whatever that meant to us at the time.  Whatever the problem turned out to be, whether it was a DH who was terrified of his own children no longer loving him, a BM who was determined to use any means necessary to cause some sort of chaos on a daily basis, or skids who had some sort of intrinsic damage already, we believed we could outlast it.  Many of us had long heart-to-heart talks with our DHs and believed we were on the same page only to find out that he folded at the first real challenge that came when BM freaked out after we said "I do." 

The bottom line is that none of us were psychic and all we can do is our best.  And sit on our hands to stop ourselves from slapping the crap out of people who say "you knew what you were getting into."

They know what they getting into.!!!!! No knows what they are getting into.   No knows that most SK play one parent against the other.  SK want there BM and BF to get back together to have the Happy Family as they knew it.

That your SO can not go no contact with there EX.  Like you can not talk daily with your EX lover. But they can, BECAUSE,  BECAUSE, of the kids. There EX is like another family member, playing with your schedule, your life.   And it just goes on and on.  But you can not be jealous!!!!

No one knows what they're getting into with any situation! Marrying someone without a preowned family. Having your own kids. Taking a new job or moving to a new city or whatever. We're not fortune tellers. Geez. I SO HATE that line!

I actually lost a best friend over this mindset because I started venting to her about ss’s BM about year into the relationship. She told me I knew what I was getting into and that any conflict between BM and DH was my fault even though I stayed away from BM and still do because it was t my place to be involved. This friend also said I should not even talk to ss because he wasn’t my kid. This was so weird to me. Now I don’t vent about BM to anyone not even DH because I get the “you know what you were getting into” comment. That’s bs. I didn’t know BM would turn psycho a year into my marriage and I didn’t know that it would get worse after DH and I started having kids. No one knows what they are getting into. Hindsight is 20/20

I had a very good idea of what I was getting into if what you're talking about is the situation on the day after the wedding.  It was really similar to the day before the wedding - skids are 4 and 6, they like me, we live in the same house, have the same routines, little has changed.  However . . .  to date BM has not been difficult to co-parent with, the skids do not seem to have much of a loyalty bind, and DH is happy because I'm fully engaged and skids and I have a good relationship.  But if that changes, if BM starts acting different because we got married, or when she gets married later this summer, if something changes the skids' attitude toward me (BM or SF's attitude, loyalty bind, the way the wind is blowing), if bringing a new baby into the mix changes everything . . . well, I really didn't anticipate that and if there are big changes I really did not anticipate, then I didn't know what I was getting into.  Does anyone REALLY know what they're getting into?   The whole thing is a big fallacy to me.

Anyone who tells you "you knew what you were getting into" about ANY life problem is not someone you want to share your troubles with.

This idea drives me crazy. By that same vein, BM's should stop complaining because they "knew what they were getting into" when they filed for divorce and, in many cases, insisted on primary custody, yet, society never seems to give them the same message. 

Divorced dads should "know what they were getting into" when they decided to get remarried and not just expect their new wife to pick up all the "mothering" duties simply because they are female. 

SMs shouldn't cede their feelings or be willing to be treated as incidental to their own lives just because the man they married had a child with someone else first. And of all the players in the situation, the stepmother is the one who was probably the least aware of what she was getting into. She didn't know all the drama, all the bitterness, all the ways that DH and BM's families would feel as if they had a right to interfere in her life. No one expects to have all these other people decide that their opinions matter more than hers should because she is not the mother to children who live in her home. No one would ever expect that and most people wouldn't put up with that, which is likely why so many blended marriages end in divorce. 

I didn't know that i would have to take responsibility of SS, i never signed up for that cause in my head the kid has his parents

I never knew SS would form stories and lies against me even after being laboured and taken care of  by me

I didn't know that DH would burden me with so many expectations i couldnt meet

I didnt know that the in laws would treat our bio child differently and stay friends with the ex and be loyal to her 

I didnt know the in laws would expect DH to put his child's unnecesarry wants above our marriage's needs

I didn't know most of our arguements and fights would be about SS

I didn't know i would feel so hurt, confused, regretful and resentful

I honestly had no idea what i wa signing up for just like a person who signs a job contract with only obvious information because they did not read all the clauses

I'll be the bad guy:

No, none of us knew exactly what we were getting in to, but some (I'd guess many) had some inkling of what would/could happen, and some even moved forward getting married with giant, bright red flags waving showing just how much of a disaster it was going to be.

I knew my DH was a Captain Save-a-Mofo when we were dating. He made great strides in correcting that behavior. So when he fell off the bandwagon last year, I was shocked and upset. However, I shouldn't have been surprised that he reverted back to his old ways. That's what is ingrained in him. I can't say I couldn't expect it, just that I'd hoped it wouldn't happen.

Yes, there will always be things we don't expect. Just like with parenting. You know you'll get no sleep the first year, but you don't realize what that actually means. It's fair to say "you knew what you were getting into" but that doesn't mean you shouldn't have empathy for that person. Unfortunately, we just lack empathy for SPs in our culture.

Really, it's not the phrase that bothers me. It's the application of it, like it absolves people from having to empathize with another human being. It absolves them from trying to understand the situation better. THAT is the far bigger problem.

Strangely, I don't go around with a crystal ball or receive psychic vibes which would have told me exactly what I was getting in to and therefore knew. Proof of this is that I ended up divorced.

Saying you have a child and your spouse has one too,  means you know about parenting is equally as ludicrous. People's parenting styles differ.There kids differ.  I have a normal parenting style with expectations and consequences outlined. My exH? He wouldn't know how to parent even if he tried... Bless him, but the man is useless and likes the idea of being liked by his kids. Whether my son like me or not, doesn't matter to me: it won't change the fact that I am his parent.

I really don't like the general unsympathetic tone, I along with other stepparents get, when it comes to marrying someone who has been married before and where there are possibly kids involved. Until one has generally walked in those shoes, you have no idea at what a step-marriage will throw at you... It's hard, it can be ugly and in the end, it can be lonely unless you get some support from people who actually understand your situation. I have come to realise that although people can try to be understanding, they really don't actually understand at all, even when well intentioned