You finish a session and you know how it felt. You don't know whether it was the right session. Those are different questions, and the second one is the one that decides your next three weeks.
How it felt is not the answer
A hard session when you're fresh and a hard session when you're two days into a head cold are the same watts and the same pace. They are not the same decision. One builds you. The other digs a hole you pay for on Thursday.
So the useful question isn't "was it hard?" It is "was it right for the state I was in?"
What you were in before you started
Four things decide whether a session was a good call. Whether you were ill or carrying an injury in that sport. How tired you already were. How big the session was against your usual training day. And whether it filled a gap, because a short easy run after four days off is a different thing from a short easy run on day six of a big block.
What it did afterwards
The cleanest way to judge is before and after. Your readiness before the session, your readiness after, and where your fatigue and form ended up at the end of the day. A session that moves readiness up and keeps load in a sensible range was a good call. One that adds a lot of fatigue for little gain was too much. One that you did while ill, or on a sore sport, was the wrong call, however good it felt.
LankFit does this for every new session after it syncs, for today only, and clears it at the end of the day. Older history is never judged in hindsight.
Knowing when you have done enough
The other half is what comes next. If the session was about as big as your usual training day, or past 100 minutes, the honest advice is nothing more today. A lighter session so far means a 30 minute top-up at most, and not in the sport you already trained. The best options for tomorrow are worth seeing, so you can sleep on them.