Hamlet wonders why he has not taken action yet, since he has all the necessary elements in place:
"Sith I have cause, and will, and strength, and means
To do it."
He is a very analytical person, who loves to break things down like this, and he lists these elements in a logical order.
Cause: you need an ultimate reason for what you are doing, a deep motivation. That is the first one he mentions.
Will: Hamlet himself does not seem to have this quality, despite his claim here. That is the missing link in his chain, perhaps. Will is the quality of persistent effort in any endeavor, or the commitment to take action. In his sonnets the bard often plays with the word will, punning on his own name.
Strength. I could not bench-press 250 lbs, no matter how much will-power I had. Strength is the actual capability needed to take action.
Means. I take means to be the pragmatic set of opportunities and techniques needed in order to carry out an action.
Of course, taking revenge for the murder of one's father is not the same as carrying out a research program. Where is your weakest link in this chain?