A.T. Robertson Commentary 2 Corinthians 11:29

"Who is weak, and I am not weak? who is caused to stumble, and I burn not?" — 2 Corinthians 11:29 (ASV)

I burn (πυρουμα). Present passive indicative of πυροω, old verb to inflame (from πυρ, fire). When a brother stumbles, Paul is set on fire with grief.