Those in charge of a unit or army can have a positive or negative effect on the morale of a fighting force.
You can find many cases throughout history where a smaller, outnumbered army has won an unlikely battle against the odds.
In 1415, Henry V gave a stirring speech to the English forces at Agincourt in France. Though the English forces were outnumbered, the use of sound tactics, the large number of longbow men, the terrain, and the likelihood for the common soldiers that, if captured, they would be killed ensured that the English were successful. It could also be said that Henry as a person added to the overall morale and effect of his forces to bring about success that day.
You can find just as many cases ...