Re: So he'd been a good employee
What Ben Tasker said.
If you own the company in a place you can dismiss people on the spot, then that's both your right and 100% your call.
However if someone has been there for 4 years and is productive for the company, then good management is to help this person improve rather than kick then out. In cases of petty misconduct (~15 hours of personal use of work machine on company time) a formal talking too might be in order, written warning if you feel the need to bring the hammer down and maybe a final warning if you're setting someone up for the chop.
People are also motivated to change if it affects their livelihood. Use that as a carrot rather than a stick . If someone really isn't wanted, find another way to make it work. Part time, remote work, come back as a contractor, take some leave or cut a cheque and part ways amicably so that down the road their skills are available, rather than belonging to an angry ex :)
Your competitors are also not stupid. One good dicking deserves another.
Management is about improving their workers. Being a dick may cause blowback.