4% Rule Confusion: Does Timing of Withdrawals Impact Long-Term Sustainability?

I’m trying to understand the 4% rule better. Let’s say I have $3 million today and start withdrawing $120,000 per year (4% of the initial balance). After three years, the market crashes 50%, leaving me with $1.5 million. Under the 4% rule, I would still continue withdrawing $120,000 per year based on the original $3 million, even though my portfolio is now much smaller.

Now, in a second scenario, I don’t take any withdrawals for the first three years. After the same 50% market crash, I’m left with $1.5 million and would have to start withdrawing 4% of that, which is only $60,000 per year.

What I don’t understand is—mathematically—why does the 4% rule allow me to keep withdrawing $120,000 in the first scenario but leaves me stuck with only $60,000 per year in the second scenario? It feels like the timing of withdrawals drastically impacts the outcome, so how does this rule account for market crashes and sequence of returns risk?