Do not boast about tomorrow,
    for you do not know what a day may bring.

This is so self-evidently true. Life can turn on a dime.

‘One of Dale Carnegie’s principles for overcoming worry is to live in “day-tight compartments.”  This term was first coined by Sir William Osler when he encountered this life-changing quote from Thomas Carlisle, “It is not our goal to see what lies dimly in the distance but to do what clearly lies at hand.” ‘

In the New Testament, James fills out the thought in today’s Proverb:

 Now listen, you who say, “Today or tomorrow we will go to this or that city, spend a year there, carry on business and make money.” 14 Why, you do not even know what will happen tomorrow. What is your life? You are a mist that appears for a little while and then vanishes. 15 Instead, you ought to say, “If it is the Lord’s will, we will live and do this or that.” 16 As it is, you boast in your arrogant schemes. All such boasting is evil. 17 If anyone, then, knows the good they ought to do and doesn’t do it, it is sin for them. (James 4:13-17).