What did Thomas Jefferson mean by “Never abandon a plan, principle, or friend” (please help)

Those things are most important in a persons life. Without them a person wouldn't survive in this world. Abandoning a plan is giving up, instead of abandoning it, make a few changes to it. Don't abandon a principle for it is a rule or moral compass that directs you into the person you are and the choices you make. At last a friend, someone to support you in the decisions you make and who can guide you or at least give advice to you, to make the right decision.

Explanation:

in his book, the riddle of the rosetta stone, james giblin talks about how there was a young british polymath and physician named thomas young who made a lot of advances on the deciphering of the rosetta stone. he says that even though young made a lot of mistakes because he was working under false assumptions, he also made huge contributions like deciphering three out of the seven symbols (more than anyone else before him). young published his findings and continued his good work but he wasn't able to progress much further due to some unfavorable situations, he still laid the basis for many other scholars and of course for the man who has been generally known to have deciphered it, jean-françois champollion