If the player fails their roll, the GM has to decide what happens - either they get the result they wanted, but suffer a condition or a twist is narrated. The obstacle does not determine the odds of being interrupted by bandits. The obstacles set out in the skill rules don't purport to be measures of anything, though: eg the fact that the Obstacles for preserving game step up by 1 for each doubling of the number of portions is a straightforward formula, but not an attempt at measuring anything. It is set by reference to the in-fiction difficulty of the task attempted - this is part of the risk/reward calculation players can perform. The obstacle for the roll determines how likely it is, in the play of the game at the table, that the player's desire for how things unfold will prevail. It is a determination-process, not a measuring process.

The roll, in Torchbearer, does not measure anything. There is no reference to odds at all, and certainly no reference to the odds of cooking being interrupted by bandits. The concept of measurement does not figure.

A and e first 48 narrator