Mace and Simmons in “Unfinished Business”

Agent Simmons?

Simmons

It's not good news, I'm afraid. The serum that's been giving you your strength... it is potentially lethal.

So you're saying it's a little risky?

Simmons

I'm saying it's Russian roulette. You've been fortunate so far, but the next injection might cause cardiac arrest. And if it doesn't, the one after is even more likely to kill you, and so on and so on until...

Jeez, don't sugarcoat it doc. [pause] And by that I mean: please, go ahead and sugarcoat it.

Simmons

I'm sorry. I know General Talbot was hoping to replicate what was done to Steve Rogers, but you'll never be Captain America.