Man in merthe, hath meser in mynd,
For meser ys treser whan merthe ys behynd,
Better yt ys to suffer and fortyn to a-byd,
Than hey for to clyme and sodenly for to slyde.

"Myrthe" - happiness, success.
"Meser"- measure- restraint.
"fortyn"- fortune.

Don't get carried away when you're on a roll; treat success and failure in a provisionary Kipligesque manner.