Lose 50% of €100 and you have €50. Gain 50% back on that €50 and you have €75, not €100. A 50% fall needs a 100% rise to fully undo it.
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Percentages are not symmetric once money is involved. A rise has to work on a smaller starting amount after a fall, so it needs to be bigger just to break even.
A 10% fall needs an 11% rise to recover. A 30% fall needs a 43% rise. A 50% fall needs a full 100% rise. The deeper the fall, the harder the climb back.
Reading "down 50%, up 50%" as "back to even" is a natural but costly mistake. The two percentages are on different bases.
Check the worst year of any fund you hold, then work out what rise it needed afterwards to get whole again.
Falls and rises are not symmetric. The deeper the fall, the bigger the rise needed to undo it.
Do it today
Check the worst year of a fund you hold.
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