Drinking – As above
Diet – “You get strong in the kitchen” If you do not eat sufficient food to have the energy to train you will not progress. Similarly, if you do not eat enough food to carry out the repairs on your muscles, you will not progress.
Stress – Increases cortisol (the catabolic {breaking down} hormone). More cortisol, less muscles. Stress also affects your mental state and ability to execute consistent training lifts.
Holidays – This is included as it’s own separate section as a result of the inherent training obstacles that they can produce. As well as not being able to find a gym, all of the above may also be included.