Gosh, there are so many that I am struggling to retrieve one in particular. As someone with a long history of mental health problems (including chronic suicidality) and just generally shitty life circumstances, I can confidently say that I wouldn't be alive now if not for the countless acts of kindness that I have been the recipient of. It's led me to develop a personal policy of extending random kindness liberally, because I know from the recipient side that what might seem like a trivial act could literally save a person's life.

It's led to a nice reinforcing cycle, in which I have been inspired to extend kindness to people who needed it, even when I was feeling out of my depth or anxious. I don't know if I'll have saved any lives, but I am confident that there are a handful of times where my actions will have left a lasting impact on a stranger. That makes me feel more connected to people, and life in general, as well as making me more open to receiving help when I need it.

Edit: I do have one instance that comes to mind, though it definitely isn't the best fit for the question — it just came to mind because writing my previous paragraph reminded me of it due to how this one small instance has shaped me so greatly.

Now I'm writing this out, it feels silly that this affected me so much, but basically when I was in 8th grade, when I was walking out from school, a cool girl in the year above me complimented me on my bright red trench coat I was wearing, saying that the colour really suited me. Although we ran in the same circles, I didn't know her particularly well at all, so this really took me by surprise.

Additional (slightly cringe, but in a charming way, because I was a teenager) context is that my school had a school uniform, and because I wanted to be seen wearing this nice new coat I had, I had made specific effort to stuff my much more convenient blazer into my overfull school bag so that I could be seen wearing the coat on my way out from school (it was spring, so not super cold). Even by regular teenager standards, I was super insecure and desperate for validation, and receiving such a sincere and unexpected compliment gave me such a boost that the memory is seared into my brain.

The lasting effect on me is that whilst the vast, vast majority of my clothing is black, there are a few splashes of red to be seen, because of how I internalised that compliment. And every time someone compliments me when I'm wearing something red, I think of this girl whose name I can't even remember, and I smile.

On top of this, I have become known amongst my friends as someone who is very good at giving compliments to people on their appearance, and who gives them freely, even to strangers. I developed this habit because of how impactful this super trivial compliment was on me when I was in an especially vulnerable place. And whenever I tell someone "I love your dress, that colour really suits you" or similar, I am reminded of how we all have the power to brighten another's day, should we choose to