In the NFL, you have a short shelf life. As a running back, if you're the first pick, and you're NFL life expectancy is only 3. 5-6 years, your first big contract might not come until three years in - well, you might never get there. They need to get those signing bonuses up front because nothing is guaranteed.
Somewhere deep down in us is stored the secret, and when we are digging in the wrong place, we know it. The secret wants to be discovered and will not let us go in peace a way that is not ours.