On the criteria of truth

Once a student asked the Masters:
- Tell me, teacher, how not to make a mistake, distinguishing true knowledge from false?
- When, walking in the desert, you see a beautiful city in front of you, what do you do to find out if there is a mirage in front of you?
After thinking, the student answered:
“There are only two ways to check this: either go to this city, or wait for the mirage to dissipate.”
“If this is still a mirage, will it not dissipate in either case?”
- Of course, scatter!
- Then do I have to go to him?
- Not.
- And if this is a real city, will it disappear if you go to it or just sit still?
- No, it will not disappear ... It turns out, it is always better to just wait! Exclaimed the Pupil.
- Or still go? - asked the Master.