What does it mean to invest if nobody consumes? Why not just work less?

Anyway, if every invests and nobody consumes, then investment itself becomes consumption because e.g. factories need maintenance even if they don't produce anything. Investments are usually self supporting, you intend to at least get your money back.

Something obvious: If investments make losses then people stop investing. There is a problem though. Buying existing real estate in popular locations is more profitable so people spend their money on something that basically provides no benefit to society. Yes, invest your money by building more housing and renting the properties out, don't invest by speculating on appreciation.

There is also another problematic "investment". Without inflation, holding onto money is never unprofitable so not only do businesses and their workers have to compete with real estate, they also have to compete with money during a recession! That is why we have some mild inflation, inflation is basically a maintenance fee on money and it makes sense because e.g. labor and food cannot be stored indefinitely.