This answer only makes sense if the asic is free.

To mine you’re investing up front in hopes that you can make enough hash profit (hash price - hash cost) to pay it off and some.

You can measure ROI in sats or dollars. (Simple numbers for example)

0.05 BTC for a miner

Makes 0.03 btc in a year but costs 0.015 in electricity and maintenance so profit is only 0.015. Takes 3.33 years to recoup initial investment assuming hash margins don’t decay and miner has good uptime.