The best laid schemes o' Mice an' Men,
Gang aft agley.
An' lea'e us nought but grief an' pain,
For promis'd joy!

(To A Mouse)

The best laid schemes o' mice an' men gang aft agley.

All human plans [are] subject to ruthless revision by Nature, or Fate, or whatever one preferred to call the powers behind the Universe.

While Europe's eye is fix'd on mighty things, The fate of empires and the fall of kings; While quacks of State must each produce his plan, And even children lisp the Rights of Man; Amid this mighty fuss just let me mention, The Rights of Woman merit

Life is what happens to us while we are making other plans.

It is easy to make plans in this world; even a cat can do it; and when one is out in those remote oceans it is noticeable that a cat's plans and a man's are worth about the same.