And sometimes the baggage are things you can do nothing about, things that happened to you or have been with you forever, and no amount of self help can workshop them away.
How we deal with the collected works of years past is important. But how someone you love deals with it all, that's what makes or breaks a relationship.
As a couple, you try to build up a world of shared history; experiences and events that create your identity together, become the amour you use to face the everyday and take on every challenge as a unit.
If you work hard and you're lucky, the everyday demands of life, the slow plod of time, shape something amazing. It produces a tight-knit, living, loving thing that you can feel just being around your partner, as well as when you're apart.
Then, one day, it all unravels. If the strain of the past - of the things you carried alone - is too much for two, the strain will eventually start to show.
When you've lived with something so long, part and parcel of your intrinsic make-up, and no longer feel it as extra weight, it can come as a shock when someone else can't handle it.
What's worse is when you've built that world together, a fortress against anything and everything life can throw at you, and it turns out to be the enemy inside that defeats you both.
The feeling is different for everyone when it happens. Akin to having the bottom of the boat cave in and water start rushing in, once it starts, it's hard to stop. And all the shared history between you may not be able to shore up the breach.
At this point, your partner either chooses you or they choose themself. To be clear, neither choice is necessarily wrong. One of them just hurts more.
You're always going to want them to choose you. Believe me, even when the relationship is dwindling, you still want someone to choose you.
Because if they don't, it means everything you put in, all the things about you and of you, things you gave to the 'couple unit', don't mean as much as their reasons to leave.
And - this is the really hard bit to get your head around - these reasons, they say so much more about that person than they will ever say about you.
Which is difficult to fathom, especially if things aren't dwindling. If they are perhaps, not amazing, but chugging along ok.
When someone chooses their life choices over yours, over the choices you thought you were making together, it creates a chasm of doubt inside.
Your rake over all the old chestnuts; was it this, was it that? What could I have done differently, said differently, been differently?
That's the rub, right there; it's not you, it's them. And not even in that horrible way that proves one of you is the bigger grown up. Just in the way that you invested more in the relationship than they did. You followed through more. You chose the life you built together over the life you could have had alone, and everything that came with that.
You chose them. With all their faults and strengths, all the frustrations and joys. You chose them.
When you pull the relationship apart, dig around all the pieces of you both, who you were together and apart, it comes down to one thing. Among all the big and little things, the ones that really matter, and the ones that totally don't.
In the end, they just didn't choose you.