People have different impressions and views regarding a coin being "potential". Either they looked at the community, future plans and developments, speculations, hypes, price movement, etc. Now, what factors do you have to call a certain altcoin as having potential?

And no, you don't have to compare each of the other altcoins to understand the potential. I don't know about INJ but surely, you do have a set of factors why you consider buying them before and now enjoying good profits the moment you sell it.

As for your final question, no one can tell you what's the exact thing to do regarding when should you sell. If you follow that coin since then, you can decide for yourself when to sell. You don't have to wait for a much higher target if you think it's good to sell it now.