Probably not the best example since once a bridge is built you can immediately use it, the benefits don't only start rolling in after a 100 years. Making sure s

Probably not the best example since once a bridge is built you can immediately use it, the benefits don't only start rolling in after a 100 years. Making sure something lasts is correlated with natural disaster safety margins anyway so if it has to be built to survive near term extremes it'll generally also survive a while as a side effect. Older constructions also seemingly last longer through survivorship bias and the lack of computer modelling at the time meant that safety margins had to be higher. A better example are maybe tree avenues that take decades to grow into anything useful, or maybe long term river redirection projects or reactors. ITER's still in construction after 16 years. But there's just about nothing we do that would take more than a few decades to start showing returns.