I was a lot like @Eforenema1 , @wpants , and @Hunter - I used to hold back bowel movements when I was a kid. I was "not too sure why" also, not completely sure anyway. A lot of it with me was because I liked the feel of a large stool in my rectum, especially when it was trying to move. But part of it became because I became self conscious about going to the bathroom after mom had discovered that I had been holding back and producing enormous stools.
One such stool in particular I had shown to her myself before I became self conscious about going to the bathroom. It had been an exceptionally big one, long and fat. I showed it to her because I had thought that it was funny, and I think I had a sense of pride in it too. Mom had kinda freaked out about it.
After that one and clogging the toilet a few times, it had become apparent that I was holding back a lot. That got me monitored, and a few trips to the Dr. after that. Then the enemas. The self consciousness about going to the bathroom grew a lot from all of this.
My mindset was very much like Eforenema1 -
I always tried to hold it in. I was not going to use the potty if I could help it. Most of the time I was able to hold it without messing my pants. Then as I held more there was no way I could hold it and some poop would get in my underwear. A very hard issue to deal with growing up for my entire family.
And like wpants -
As someone who was also very anxious or shy about using the potty sometimes I'd keep trying to hold it until I just couldn't and refused to acknowledge to anyone I needed to go at all and certainly would not actually go to the toilet.
I was told or reminded every evening to "make a poopy" because I wouldn't go to the toilet on my own either. I got pretty good at holding back part of it though, often to the point that I'd eventually get constipated and couldn't go. If I couldn't or wouldn't go, I'd have to get an enema.
I used to try to hide when I was holding it, and like all of these guys who had posted here, I frequently messed my pants. I didn't have a particular place, just somewhere I wouldn't get caught crossing my legs (often the basement). Whenever I was caught doing it I was ordered straight to the toilet. If I "didn't make a poopy" there woud be an enema, usually a bag enema.