Ever tried to drink tea from a cup that is partly filled with coffee?
Even though you may come up with an interesting drink (that is if you don't puke your guts out
), you will still not be able to tell or appreciate either the tea or the coffee. In fact your tastebuds may become very confused.
If nothing else, the taste of either beverage is pretty contaminated, you may become disgusted, possibly to the point of emptying the cup, cleaning it, and then trying again with either drink separately.
At this point you may decide that the previous mix tasted better, or that you prefer the separate tastes that may give you better insight into how to mix the flavours. Then you can take an even bigger cup and mix them both in proportions that taste (and work) the best for you.
Training is sometimes like this.
Just my 2 cents.