My sell rules are a work in progress as I collect trade stats (just started really trading stocks in earnest last month). Thus far, my average loss is 3% stock trades (not account). Selling half at 5 x my average loss is a wise thing to do so I don't end up in a situation like what happened with another one of my trades where a great profit turned into a BE trade.
Your VTSI trade is a great example of a good trade with a bad outcome. You ended up with a better outcome than I would have as I would have taken the trade off under the swing low. It's one trade out of many and there wasn't much you could have done differently. It's a successful trade if you followed your plan. You can't control what the price does you can only control what you do. Good trade!!
For VTSI, I could have sold half my position at a profit somewhere between a 15 to 25% gain. This is not the only approach, but it fits my phycology and the fact at a little over one month of trading like this I already have 15 trades. Based on my trade count and metrics thus far, I am not reliant on a few big winners and it makes sense to nail down some profits sooner rather than later.
As previously mentioned....my sell rules are a work in progress. Just started trading in this manner a little over a month ago. My typical style of trading is via algos trading futures.
Still doing futures. My capital utilization rate is crazy low with my futures algos. Got tired of seeing my capital doing nothing when it could be deployed to other opportunities.