You can influence you counterpart’s choice by wisely framing an offer.

Example A:  Choose either option 1 or 2:
     Option 1:  You receive $1000
     Option 2:  There is a 20% chance you will receive $5000 and an 80% chance you will receive nothing.

Example B:  Choose either option 1 or 2:
     Option 1:  You lose $1000
     Option 2:  There is a 20% chance you will lose $5000 and an 80% chance you will lose nothing.

When faced with certain gain or the possibility of a greater gain/no gain, people will be risk adverse and choose the certain gain (see example A above).  On the other hand, when faced with certain loss or the possibility of greater loss/no loss, people tend to be risk-takers (see example B above).

So how can you use this knowledge to your benefit?  Frame your offer as a gain so as to induce your counterpart to see your offer as getting a benefit rather than avoiding a risk or loss.