It could have been 'Unless you push the envelope, you will never know the limits!' It means basically that unless you push yourself to higher achievement, then you will never know your limits. In much the same way, test pilots push aeroplanes to their limits, pushing the envelope, to discover the true potential of the craft.
sorry hit wrong key. were tought is that unless u break away from your daily routine and push your boundries youll never know your potential.hope this helps.