This quote is often cited as being from the Buddha, and is found in several books:
What you are is what you have been. What you will be is what you do now.
The first instance I know of (thanks to a helpful reader) is in Sogyal Rinpoche’s “Tibetan Book of Living and Dying,” which was published in 1992. I’m not sure where Sogyal got it from, but it’s simply not the kind of thing that the Buddha said and it doesn’t come from the Buddhist scriptures. I suspect that Sogyal was simply paraphrasing the Buddhist teaching of karma and that he (or his editor) chose to present his paraphrase as a quote.
The quote is also internally inconsistent and incoherent. For consistency it should really say “What you are is what you have done. What you will be is what you do now.” The theme would then be that our actions shape who we are, which is a thoroughly Buddhist notion. Instead the first part of the quote is saying, in effect, what you were is what you are, which implies that you haven’t changed. The logical inference regarding the future would therefore be “what you are now is what you will be in the future.” That’s why I describe the quote as incoherent.
In fact, there are a couple of instances of the quote in the “what you have done” form, but the vast majority are “what you have been.”
The Buddha did stress that we create ourselves through our actions. He even, in an oft-repeated statement, metaphorically suggested that our actions give birth to who we are: “I am the owner of my actions (kamma), heir to my actions, born of my actions, related through my actions, and have my actions as my arbitrator. Whatever I do, for good or for evil, to that will I fall heir.”
He also, however, flatly contradicted that our entire experience is defined by our past:
So any brahmans & contemplatives who are of the doctrine & view that whatever an individual feels — pleasure, pain, neither pleasure-nor-pain — is entirely caused by what was done before — slip past what they themselves know, slip past what is agreed on by the world. Therefore I say that those brahmans & contemplatives are wrong.
The point is that our present moment represents the confluence of what we have created in the past, with our present actions. To suggest that we are entirely “what we have done” is to ignore the possibility of our choosing, right now, how to relate to experiences that arise from the past.