Blade Life
You are changing your blade less often than you should. That is almost certainly true.
The Number Is Lower Than You Think
For fine cut-paper work — anything under two millimetres wide, any curve, any edge you want clean rather than dragged — a blade is sharp for somewhere between ten and twenty cuts. Not ten and twenty sessions. Ten and twenty cuts. Maybe a few more on forgiving stock, fewer on anything with significant tooth or sizing. This is not a counsel of extravagance; it is just the arithmetic of what a fine blade is actually doing.
A fresh blade separates fibres. A dull one bullies them apart. The difference is not dramatic until you look at the edge under a loupe, and then it is unmistakable: one is a wall, the other is a tangle. That tangle is fringe — those ragged wisps at the border of a cut that feel like a failure of skill when they are almost always a failure of maintenance.
A blade is sharp for ten to twenty cuts, not ten to twenty sessions
What Dullness Costs
Pressure is the first thing to go wrong. When the blade is not cutting efficiently, you compensate by pressing harder — often without noticing. Harder pressure on a lightweight sheet means the paper moves, or the mat drags it, or you overshoot a corner. Harder pressure on a heavier stock means the blade is following the grain instead of crossing it cleanly. Neither outcome is recoverable. You can retrace a line but you cannot un-tear a fibre.
The second cost is accuracy. A dull blade skates before it bites. That fraction of a second before engagement is enough to take the line half a millimetre off its intended path. At any scale, half a millimetre compounds fast.
The third cost is your hand. Sustained extra pressure across a session is tiring in a way that a sequence of light, confident strokes is not. By the end of a long cut you are gripping harder, steadying against the blade's resistance, and the last ten centimetres of any line show it.
The Habit
Change the blade before you think it needs changing. That is the whole instruction. A box of replacement blades is inexpensive; a ruined sheet is not. If you are uncertain whether the blade is still sharp, it is not. Uncertainty about sharpness is itself the sign.
Dispose of spent blades safely — a rigid container with a narrow slot, or the foil-capped tube many blade boxes include. That part is not optional.
The work is already hard. There is no reason to make it harder with a blade that has done its job and deserves to be retired.