Math isn't biased. Flawed reasoning is. For x ≠ 0

(1 + x)(1 − x) = 1 − x² < 1

The correct way to cancel scaling by a proportion is its reciprocal, ie, for x ≠ 0

x ∙ ¹⁄ₓ = 1

A 10% decrease is ⁹⁄₁₀

100% − 10% = 90% = ⁹⁄₁₀

Its reciprocal is ¹⁰⁄₉, a ¹⁄₉ = 11¹⁄₉% increase

1 / (100% − 10%) = ¹⁰⁄₉ = 100% + 11¹⁄₉%

We make it complicated by stating increase/decrease & percent instead of simple scaling factors. The western world has a weird 💯 fetish almost as funny as ancient mesopotamians and the number 60.

In general, for proportional change x, the proportional change y to cancel it is the solution of

(1 + x)(1 + y) = 1
y = (1 + x)⁻¹ − 1