Belief.
Although the budgets, heritage, history, bookmakers, media and pundits may all say it can't be done, belief is one of the big keys to overcoming what appears to be the near impossible.
Anyone who was regularly close to the Dundalk squad in their European exploits, can tell you that Stephen Kenny installed almost incredible levels of belief in his players that they could overcome teams like Bate, Macabbi, Legia, Zenit, Alkmar, Rosenborg, Alkmaar and Hajduk. The players absolutely believed that they could win against these teams home or away.
It may not have always have proved to be the case, but it always gave them a real chance.
Legia Warsaw can be beaten