I don't think it's as simple as me not being a dick
It isn't. A MIL/DIL pairing is like any other. What it is going to look like cannot be controlled by one half of the equation planning on behaving in a certain way. And unfortunately that is going to mean some people (who think they have their future MILdom sorted) are going to get a nasty shock. Not least because planning on being as near as you can get to paragon of virtue status rarely pans out once human frailties (on both sides) are factored into the mix.
I think 3 ? of us as DILs on this thread have raised our hands to having properly contributed, or been responsible for, some/most of the tension in a DIL/MIL relationship. Just 3. Say six in case I missed some. In forums largely populated by older women, you'd likely see just as few MILs raise their hands. It does seem to be that this is one relationship where there is a notable amount of disinterest in taking a long hard look at oneself and being willing to take some responsibility for one's own feet of clay having left some muddy footprints over the relationship's history and evolution.
Back in the real world, occasionally it's almost all the DIL, occasionally it's almost all the MIL.
Sometimes it's just a pure personality clash. Never going to work. Stay the fuck out of each other's way while the rest of the family get on with it is the only workable solution.
But more often than not both sides have justified niggles. Just like in most other relationships. In some cases there is (more or less) a joint effort to keep things down to niggle level. In others, one or both fan the niggle sparks and both MILs and DILs can get a bit "let me once again count the reasons, no matter how petty, why you irritate the fuck out of me and are therefore a dick, so I can justify being a dick right back at you".
Hopefully most of us will get to be in the "get on like a house on fire" to "well controlled, non exaggerated, non over egged niggles" range of DIL/MIL situations.