Let’s say E is everyone’s second choice, but nobody’s first choice. E is the first candidate eliminated because E got 0% of the vote.
Let’s say it shakes out like this:
40% A E C B
21% B E A C
20% D E C B
19% C E D B <- You
40 A D 39 D B 21 B D
60 D 40 A
First round, E is eliminated despite being the most popular candidate by far.
Second Round, C, followed by B. D wins.
But if 3% of A voters switched to C, then A would have won because D would be eliminated, sending their votes to C, which would have eliminated B, sending those votes to A. But D and C voters hate A, so it’s in their best interest to also vote for B. And now we’re back to fptp
When considering the quality of a voting system, you want voters to be honest (i.e. not strategic in their votes). Voters should pick the candidate they agree with, not the candidates they think they must support to avoid a catastrophe.