I think everything has been said.
- Habit, taken off before fully loaded, will manage this time too
- Performance figures are for new aeroplanes, most times we fly old clapped out engines.
- Pilot proficiency from short fields, and ability to judge grass length, also taking in to account if wet
For British pilots temprature and density altitude maybe a major unconsidered factor.
Flying in central Italy my aircraft performance changes considarably depending if I'm taking off sea level or from a strip in the Appenines, and even more so if in winter or summer.
In summer with 30° plus temprature I simply double take off roll if at sea level.
If in the mountains when hot I refer to the POH charts, consider full load even if light and add 20% scare factor. And even so, sometimes I scare myself.