Edit: I did it!
Yes, definitely an issue with newer drivers or drivers who aren’t attuned to the limits of the kart yet or aren’t consistent yet.
Data can be very helpful with this because you can look at split times or even just the GPS trace and see if you did something wonky in one corner that had a big effect on lap time, as @oldguy was able to do in his thread. Or you can just feel you made a mistake as a driver, and that explains the lap time difference. Sometimes I’ll come in and whoever I’m with might say “looks like that didn’t work”, but as a driver I remember that maybe there was a mistake on my best lap or something, and up until that point the change felt better, so I keep it, even though the lap time doesn’t look better.
As with all adjustments and driving things, they work in tandem. So I wouldn’t say necessarily to focus just on the feel of the kart with each adjustment. That’s part of it, but the stopwatch is part of it too. Taking a broad view on your overall lap times for each session and judging adjustments on how they performed over a whole run is a good idea, if you feel you aren’t being consistent enough to make a call on how the adjustment worked.
And this isn’t just an issue with newer drivers either necessarily. I know there are times where I make a small tweak and I am not sure how I feel about it after a session, or maybe my lap times didn’t change much. Maybe I didn’t feel I put a good representative lap together, or I made a mistake on my best lap or something, and I want another session to really judge the adjustment with a little cleaner run.