I have certain memories that are crystal clear, mostly traumatic, from ~2.5-4yo:

• When I fell off the couch and hurt my dog by landing on her, resulting in her snapping at me and getting bit on the face (required significant reconstructive surgery and rehoming the dog to a family without kids just to be safe, which destroyed me and my dad who loved her dearly)

• Getting chased and bit by geese at the farm-style day care my parents sent me to before preschool

• When I got a Streptococcus infection in my forearm growthplate and had to spend a lot of time in the hospital and had a port in my chest for direct medicine administration to my hear

• When I put an unpopped corn kernel in my ear and had to go to the ER to get it removed (the one day where both my parents' insurance had lapsed. My dad was starting a new job the next day, naturally, though I didn't understand that at the time obviously)

• Being scared of my great grandma when she was dying in the hospital with all the tubes and her sallow, paper skin

• The first (and only time) I got spanked, by my dad, which ended with me peeing myself and my mom shouting at him until early in the morning (he wasn't abusive or anything, just a young dad who thought it was appropriate based on his upbringing that never did it again, apologized profusely to me and my mom, and still feels terrible about it)

I remember other, more positive, things from those ages, but not with the clarity or specificty that I recall these events. I remember watching the pokemon anime with my dad on the couch when he slept in after working the night shift, him making characters for me and teaching me how to play computer games via Everquest, my mom taking me to work with her when I was sad about not seeing her a lot, being with my aunt and cousins who lived just down the road, chasing garter snakes in the yard, etc.

I think it is like the red-light/green-light effect when driving: you are more likely to notice all the red lights you hit when driving because they negatively impact your normal routine, but forget the green lights that facilitate the routine. The positive memories become the general feeling you get of the time, the green lights. The bad memories stand out because they were disruptive and different, harsh red lights in your younger years.