The default lot size is a trap waiting for a tired brain

[Shadow Trader]

Opening the order window and finding it prefilled with last session's size. Or a default of 1.00 lot on an account that normally trades 0.10. The hand clicks without the brain noticing.

It seems like a small thing. It isn't. Size errors are among the most expensive operational mistakes, because everything else about the trade can be right and the result is still painful.

Platforms differ in how they handle defaults. Some remember the last size used per symbol, others have a global default, and some change when switching account types. After a platform update or a reinstall, defaults sometimes reset to something unexpected.

Good habits are boring. Set the default to the smallest acceptable size, not the usual one. Use position size calculators with fixed risk. Confirm the number on screen every single time before clicking, especially after a break or when switching charts.

A related trap is units: some platforms count in lots, others in units or thousands, and mixing them up leads to orders 100 times too large or too small.

What default size is set on the platform, and has it ever been wrong at a bad moment?