One of my favorite proverb is "When the water rises, hurry to collect some." It's often said when the opportunity came to life. I harvest Before that chance slip away. means that when there is a good chance that came through to take the opportunity and benefits fully. Before this great time period elapsed. A similar proverb in English is"Make hay while the sun shines." I like it because it can make my decision easier. To get a chance to came to life without hesitation.