ROI stands for return on investment, meaning how much you get for what you put in.
Time is arguably the most valuable asset, and what I continue to find is that those who increase their income tend to buy back their time.
An exercise I started to practice a year ago was putting a monetary value on an hour of my time. For example, if one hour of your time is worth £15, then anything that costs less than £15 that saves you an hour is a good investment.
This can also be applied to outsourcing your time to other people, if you're building a team for example. If one hour of your time bumps up to £30, then hiring someone for £15/hour is a good investment, as you buy back £15 worth of your time.
On the flip side, if an hour of your time is worth £30, doing a job that pays you £15 an hour is no longer a good investment - unless it's providing you with opportunities or another form of return.
This is also something that must be considered on a larger scale when committing to major life decisions, university for example.
What return are you getting for £40,000 in debt (the average student loan debt) and 3+ years of your time?
This doesn't have to be singled down to the monetary return (how much more money you could make) but also the experiences, opportunities, people, and a platform (being given money to live on) to take risks.
In those 3+ years, you will spend countless hours of your time on your degree. When you TRULY take a step back and think about just how much time that is, what else could you have done?
So, take a step back before making both day-to-day and major life decisions, and ask yourself: "Is this worth my time?"