Is it really easier to decrease your overall grade in a class than increase it?

Question

I was thinking about how grades work. Obviously most people’s grades are weighted, each type of assignment holds a different value and exams usually count for the most. People always complain about how when they get good grades their overall grade barely increases and when they get bad grades, their grades tank. That got me thinking and I came up with the scenario below.

If I have 5 assignments and the average is 80 and I get a 6th assignment one of 3 things can happen:

1. I get below an 80, my average drops
2. I get an 80, my grade stays the same
3. I get above an 80, my grade increases

Say I get below an 80. If I get a 70, the new average is 78 and 1/3. So, the average decreased by 1 and 2/3. If I get a 90, the new average is 81 and 2/3. So the average increased by 1 and 2/3 (the same exact amount).

So I immediately thought that idea is bullshit. But I’m wondering if maybe I’m wrong. Here are some factors I thought could prove me wrong:

1. The consistency of the grades (an average of 50 can mean you have all 50s or you got an equal amount of 100s and 0s, so maybe if you get a 90 in one scenario, it changes your grade differently than if you got a 90 in the other scenario)

2. The amount of assignments (if you have less assignments, that’s great if your grades are good but if you do badly even on one, your overall grade can suffer)

3. How much the assignment was weighted (if you did badly on an assignment that’s 5% versus 10% will affect how much your grade drops)

Answer 1

As you rightly noticed, there's no mathematical bias keeping an average low.

However, the difficulty of obtaining the grades necessary to alter your average may be the cause of the perception that an average is easy to lower but hard to raise.

If you already have an average of 80, you need a high mark with a significant relative weight to your existing average to significantly change that average. In most cases, you'd need to get 90+ on the concerned assignment, which means cutting your failure rate by half, which is no small feat. One might even consider it equivalent to being two times better.

On the other hand, lowering your average by an equivalent amount is easy: you just need to get 70-, which is easily achieved by having a bad night of sleep and misreading an exam question.