What is the meaning of "count your losers" at no trump, and "count your winners" for a trump contract?
Typical advice is exactly the opposite. See:

https://www.google.com/search?q=count+winners+losers+trump+notrump

"In trump suit contracts, we count losers. (In notrump contracts, we count sure winners.)"

This is a simplification, but with a trump suit you can often ruff when you cannot win tricks with high cards or set up intermediate or long suit winners. Take for instance:

S 98765
H 2
D 32
C 65432

S AKQJT
H 5432
D 432
C 2


In a spade contract you have 1 heart loser, 2 diamond losers, and 1 club loser, so all being well you might come to 13 - (1+2+1) = 9 winners. If you draw too many trump, though, or your opponents realize that they should lead trump, you will come up short.

This might not be a realistic example since your opponents can take 12 tricks in hearts or diamonds...