Why should I not open ports to the internet on my home router?

I'm in the process of setting up homelab stuff and i've been doing some reading. It seems the consensus is to put everything behind a reverse proxy and use a vpn or cloudflare tunnel.

I plan to use a VPN for accessing my internal network from outside and to protect less battle tested foss software. But I feel like if I cant open a port to the internet to host a webserver then the internet is no longer a free place and we're cooked.

So my question is, Can I expose webserver, SSH, WireGuard to the internet with reasonable safety? What precautions and common mistakes do I need to watchout for.