A budget built from your actual numbers rather than a rule that assumes a household unlike yours — plus tracking you'll realistically keep up and an honest answer if the numbers simply don't balance.
What if it turns out you've been wasting a lot? So the statement goes unopened and the number stays unknown — which is reliably worse than whatever the number actually is.
Connect the accounts, sort fifty categories, correct the miscategorised ones every week. It fails on effort rather than on discipline, and then it feels like a personal failing.
50/30/20 assumes needs fit in half your income. On lower incomes and in expensive areas they routinely don't — which makes the rule feel like a verdict rather than a starting point.
Usually because they had no slack in them, so the first unplanned cost broke the whole thing. A plan with room in it survives a normal week.