OK, so, you know (or you may not) how when you're in the desert, and it's approaching midday, the temperature just rises, and rises? Imagine the hour around midday not being an hour, but 10 days. Insolation, even at our distance (remember, inverse square law), is punishing. On venus, it's ridiculous.

Venusian colonisation will have to be sub-surface, even if we cover it in water - at least until if and when we come up with a gigantic solar shield that can filter and weaken a planet's worth of sunlight.