"If we fight we may not win, but if we don't fight we'll surely lose."
I'm not sure where this quote originates from, but I am fairly certain I have seen Unite GS Tony Woodley use it at some point. And much as I am a weedy moderate, and generally dislike combative language, I think it works quite well.
One of the reasons for this might be that it taps into loss aversion, our strong instinct to try and avoid losses. This is a really key concept, and greatly clarifies understanding of how people assess risk. As the Wiki link explains we 'feel' losses more strongly than we do gains. This means the way that we approach gains and losses differs. We tend to favour limited certain gains over greater possible but not guaranteed gains. But we try to avoid a guaranteed loss, even if this means taking on the risk of a greater possible loss.
Isn't that exactly what the slogan at the top is doing? It is saying it is better to take a risk that might mean you manage to avoid a loss, than to accept a guaranteed loss. As such it is likely to have quite a bit of emotional pull.