I'm a huge fan of Amazon Prime and more recently Amazon Prime Pantry. My 57 Amazon Prime orders in 2014 bears this out. Ok I'm an Amazon junkie, I admit it.

Using Amazon Prime Pantry once a month has supplanted one of my semi-monthly trips to Costco and probably one of my weekly trips to the grocery store. This is an example of obvious or direct competition — in this case, Amazon Prime Pantry is taking my business away from Costco at least once a month.

Yet in thinking about how my shopping habits are interrelated, it dawned on me that some of these relationships are not always direct and may come from less than obvious places. This type of relationship is what I call "strange competition".

Let me give you an example. Continuing on my home delivery kick, I recently started using Instacart for same-day grocery delivery. I go online, shop each store through their site and then Instacart sends out personal shoppers to Whole Foods, Costco and select other grocery stores in my area then delivers my order(s) the same day. It's awesome, especially since I don't have a car.

In this case, the specific stores are not directly competing against each other — each store is getting a normal order from me. The loser here is Zipcar. Zipcar is a car sharing service that allows you to rent cars by the hour which I often used to do my shopping runs. Yet, every time I use Instacart, I'm not reserving a Zipcar and they are losing business.

As I am doing more and more shopping online, my need (and desire) to go to physical stores diminishes. As a result, the once a week Zipcar shopping runs are now once a month at most. This strange competition from Instacart is not something Zipcar could have predicted and now that it is here, how will they deal with it? I don't have the answers but these type of unpredictable relationships will become the norm as more shopping moves away from brick and mortar stores.