Context, my family is upper middle class, though my parents were technically not when I was little (my dad was a college professor in Ireland which was a very poor country at the time, so high prestige and low pay, and my mom gave up her nursing career when I was born). My mom's side was poor (Irish) and my dad's side was very well off (grandfather founded a successful market research firm and ran that for decades in NYC).
My grandfather paid for my college, it was deeply meaningful as it let me go to the school I wanted to and graduate with no debt, which was a great starting position. When he and my grandmother on the other side passed, I inherited low six figures from each which was a VERY meaningful bump to my investments at the time (about doubled them). My parents started gifting the annual max to myself and my brother about 15-20 years ago, which has been extremely meaningful, the marginal utility of those dollars at the amounts I made as a video game designer were very high, enabling me to do more than just max my 401k contributions (maxed Roth when I qualified and had non-tax advantaged investments as well). Even now when my finances are pretty secure, it is appreciated and helpful (my current job is about to go away probably and this year's gift makes that much less urgent a situation). And importantly my parents started doing it because they wanted to pass on our inheritances when it would make a more significant impact on my brother's and my life, and while they were alive to see and enjoy the impact their gifting was having on our lives.
The keys that made this all work I think:
College not costing anything for my brother and I directly didn't spoil us because we were already used to the idea that family paid for us to get educated. Our job was to make the most of the learning opportunities. The starting debt free was an invisible benefit that wasn't like we were being given recurring handouts once we were working adults. Amusingly, years later, I realized I probably would have been better off going to a cheaper school and having been given that money to invest, heh, but then I wouldn't have had the experiences I have had and become the person I am, so... who knows?
The inheritances felt like a one-off thing and happened at a time in my life where I was already along my way investing to my first million. It felt like a confirmation of the path I was on, not a pile of unearned money to be spent frivolously
The annual gifting my parents waited till my brother and I were both adults in our 30s, established in our careers with a track record of responsible financial behaviour. The money made a significant marginal difference to me earlier, though was less significant for my brother who was in management consulting. In more recent years it was more significant for my brother who was no longer managing 200 consultants in a firm and trying his own startups, and less so for me, but the overall effect was to smooth out rough times and help us along, without us feeling entitled to it, or reliant upon it.
I think it matters that we got money in ways that didn't make us feel dependent or create expectations initially, and then later money came after we were already showing we were financially responsible people. I fully expect to inherit significant amounts from my parents when they pass but hopefully that will be long after it would make any difference to my lifestyle as I'd rather have my parents for as many more decades as possible than bump up my financial escape velocity point. And if they manage to spend such that they die with zero, I will be happy as heck that they had a fun set of decades, though that outcome seems unlikely given they feel flush enough to make annual gifts.