How to find motivation to overcome a hindrance in the moment of truth? I am trying for a long time to find motivation to practice meditation - i think i found a good general motivation finally after watching a dhamma talk  

but it still doesn't fully solve my problem  :      when i have the hindrance show up - how to overcome it ?  hunger - tiredness - pain - cold ect  

now people can say : "just be mindful of it and let it go"    BUT  .....   how do i find motivation to be mindful at that specific moment ?  i can be mindful for half an hour meditating being mindful  but what should i do when i become very tired or very hungry - where its very hard to stay mindful - what gives me the power to overcome it than - how to find motivation to be mindful at that specific hard moment ?
the only motivation possible is the internal readiness to cultivate the mind and the virtue, understanding that this is what's the Noble Eightfold Path is about

the motivation to follow the path proposed by the Buddha comes from the very understanding of the 4 Noble Truths at least at the intellectual level

so if one does have desire to end suffering they'll follow the path which facilitates attainment of that goal, and strive for proper maintenance of mindfulness

if such understanding and desire are not there, then there's no point in forcing oneself and looking for other types of motivators

speaking of hunger, it's the same as forcing oneself to eat without being hungry or even have an appetite

if one understands the concept of suffering but the understanding still doesn't engender enough will power to follow the Path, there's a good chance that the understanding isn't profound enough and so more reflection on suffering and its ubiquity is probably required

here maranasati may come in handy to develop a certain degree of samvega

Maranasati sutta 1 (AN 6.19)
Maranasati sutta 2 (AN 6.20)

in the Capala sutta (AN 7.58) the Buddha instructs Ven Moggallana on the strategies of dispelling drowsiness during  meditation, which may be of help in cases of waning mindfulness 

in the Vitakkasanthana sutta (MN 20) the Buddha explains how to counteract unskillful mental states with appropriate attention

in the Aggi sutta (SN 46.53) he explains what mental states are appropriate for development of certain factors of awakening