he who hesitates
he who hesitates (is lost)
Those who fail to take quick, decisive action will suffer for it or miss a good opportunity. A: "If only I'd invested in that company when they started up, I'd be a millionaire by now!" B: "Well, he who hesitates is lost." A: "You could have mitigated your losses if you'd dealt with the problem right away, but—" B: "Yeah, yeah, he who hesitates. I know."