What, How, and When & Whether

It is common for a PO to get deeply involved in What, How, and When.
And it is very correct too.

But PO is responsible for something else which is far more crucial than all the three above.
That "something else" is "Whether", and it comes even before What, How, and When.
Seeking an answer to "Whether" needs Outward Focus.
Outward Focus is of course crucial throughout the product life cycle, but it is million times more crucial before you commit yourself to a risky initiative like building a product.

When it comes to building an intangible thing like a software product, however hard we try, we can not bring down the risk level to Zero. All we can do is try to foresee potential risks and try to reduce risks.
Building a Product Vision Canvas helps us to reduce the risks by validating our hypotheses.  

Hypotheses like...

• The problem we are trying to solve
• The Unique Value our solution aspires to offer
• The way customers are managing their life in the absence of our solution
• Market and size for our solution
• Our cost and revenue projection
• The runway available for us

As Steve Blank says... Nothing-Important-Happens-In-The-Office (NIHITO), it is crucial that PO validates the above hypotheses with a sharp outward focus.
It is a must for PO to seek inputs on these hypotheses from the market/prospects/trade shows/SMEs/etc, and discuss/brainstorm with as many stakeholders as possible, and rate her confidence level for each hypotheses herself when she validates these hypotheses.

The real magic happens when one puts a pen on paper.
Self-rating the confidence level of each hypotheses validation is exactly putting pen on paper.

Something like this...

Generally, we (we all humans) find it easy to give a rosy picture to others as well as to ourselves while we are talking. 
But when we put a pen on paper, (of fingers on keyboard), the invisible parser in our mind kicks in, and we find it comparatively difficult to present a rosy picture w/o sufficiently validating it.  That is just the way, the human mind works. Why not make use of it?

When your system nudges you to validate your hypotheses and rate your confidence level for that validation, it helps you to take a bit more educated decision on "Whether". 

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Let me know if you like this/find this useful.
Surely let me know if you disagree.