Thanks a lot for your questioning and motivation 
Selling, high or low, is an issue. Early in my financial life I sometimes sold when I tried to speculate and panicked whether to secure gains or stop loss. The stress vs. Performance and 0-strategy was quite a 0-sum game, but we’re talking almost “teenager trading” and in the end, no loss of the few thousands I played with 
I have increased my risk tolerance by understanding and being comfortable that I buy something when buying assets, i.e. the stock (if stocks) is the currency as we often describe here. Sometimes it’s cheap, sometimes it’s more expensive, but it’s an active asset hopefully creating value. That is why we invest, isn’t it? If I own 100 AAPL, I will own 100 AAPL tomorrow, whatever its price.
Others buy fancy cars (losing value
), I buy stocks/x/y/z.
So selling is an issue because it is not in my algorithm and mindset in the first place when I finally committed to investing.
Then there is a question everyone could relate, because I read a lot about the “fun money allocation”. Everyone hopes it can work, that’s not just adrenaline. What if fun got funnier and suddenly is 25% of your NW ? Good luck contributing to your core portfolio to get it back to 5%. But you’re at risk to lose all your gains if you do nothing … or fomo.
Or maybe you bought gold and were lazy to rebalance, and got over performance these days and now your asking yourself, “well that laziness paid off, is rebalancing really a thing?”.
Selling if robo does it is no issue, I did exactly that, tested it with a small amounts. Similar allocation, minus fun money… and guess what… enjoyed doing nothing and stress level down about it. And I know it’s there, available, for deposit of any size or withdrawal, and pushing the buttons on its own to get a rebalancing premium (hopefully) and stick to the rules I defined. Started beginning of 22, bad year, and certainly the best tool to make me invest even more in these conditions, and forget about it. Is it because of small amounts I feel ok about it ? Small aum so quite small fees as well ? Maybe.
It may teach me that it works ok for me so “just trust your guts and your rules and push the buttons yourself in the core portfolio”. And double check so you don’t add/miss a 0 when placing the order (credits to @Moustachienne
).
Thanks!!!