A cyclohexane ring is not flat — it puckers into a chair. Every carbon carries one axial bond (straight up or down) and one equatorial bond (splayed out around the rim). The ring flips between two chairs about a hundred thousand times a second, and each flip turns every axial bond equatorial and vice-versa.
An axial group is cramped: it points straight at the two axial hydrogens two carbons away on its own face — the 1,3-diaxial interaction. Equatorial is roomy. The energy cost of forcing a group axial is its A-value: 7.6 kJ/mol for methyl, a commanding 21 for tert-butyl.
Where the ring spends its time follows K = exp(−ΔG/RT), with RT ≈ 2.5 kJ/mol at room temperature. Methyl's A-value gives K ≈ 21, so it sits equatorial ~95% of the time. tert-Butyl is so large it locks the ring — chemists bolt one on as a conformational anchor.
Two groups can cooperate or fight. trans-1,4 lets both sit equatorial at once — no penalty. cis-1,3 pins one chair diequatorial because the other would slam both groups axial on the same face, a real 1,3-diaxial clash. The flip never stops; only the odds change.
Something in the simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.