Didn't you know that?
Well, it is true. You are a scale. You need to measure things. Specifically, you need to weigh projects to determine how heavy they are.
Because you are also the person who is likely responsible for assigning those projects to someone (or some team) to deliver results.
Here's the challenge. Is your "scale" calibrated? How accurate is it? A scale that doesn't measure accurately isn't very helpful.
Let us assume your scale is accurately measuring the weight of your school projects. Now what?
"Light" projects are those that should not present a problem to just about anyone on your team. Successful completion does not require any major use of energy or necessitate any specialized skill set. For example, let's say you need someone to monitor a study hall. Just about anyone can be present in a room and supervise students for a brief period. That would be an example of "light lifting." No particular level of "strength" needed to successfully complete that task.
I think it is important to point out that "lighter" projects may not be less important. Using my example, if nobody supervised study hall there is potential for huge problems. Just because the task is light, doesn't mean unimportant.
These tasks are more involved. They require more insight, specialization, experience, etc. for successful completion. The heavier the task, the stronger the "lifter" needs to be. In other words, you should assign your stronger team members to the heavier projects. Heavy projects also require more involvement.
Using the lifting metaphor, heavy projects should also have "spotters" set up to help. One of those spotters should be YOU. As the leader, you need to support those projects and have a stake in their success.
Do not turn away form the heavy lifting! Be there to support the team's efforts.
How To "Get Stronger"
Now, a question you may have is, "If my stronger team members are the only ones doing 'heavy' work, how do the others get stronger?"
This question is a good one because, as with working out, the only way to get stronger is to gradually add more weight.
That is exactly the same approach in building your team members' strengths.
Look for ways to include your "weaker" members in heavy tasks by asking your "stronger" members to mentor, coach, and guide them with heavier work.
A note of caution: Always be aware of signs of fatigue. ALL team members will get tired. Even your stronger individuals eventually wear down. Be prepared to "stop the lifting" for a while to celebrate success and allow people to re-energize.
And of course, keep your back straight and lift with the legs!