I am sure you have all head your parenting nemeses... something you found difficult to crack.
For us (DS1) - sleep amazing, weaning/food ok... but... the toilet training. No 1s went ok actually, but then DS was in pants and had not yet cracked No 2s . And I was due DS2 any time and sick and tired of cleaning up the mess.
Eventually, what cracked the problem for us was surprise eggs. I realised at the time that this is what he really, really wanted. So after nursery one day I promised him a surprise egg if he did a poo on the toilet or potty.
Cue an evening of squeezing and trying... just for nothing to come, followed by a mighty tantrum as it was time to go to bed... without the surprise egg.
However, he did remember the next day and worked hard for his egg and of course got it! On my first day of mat leave I then created the big poo reward chard that involved surprise eggs at every successful attempt and bigger gifts at various intervals.
About 20 surprise eggs later he were in a good pattern of "going for a squeeze" every morning and evening. DS1 was smart... if there was one going in in two pieces he would demand two eggs !
So... how did you crack the things that you found hard?