Based on the Gemara, the Shulchan Aruch says the following in Siman Reish Vav, se'if Dalet (section four): for anything you are going to eat or smell, you have to hold it in your right hand when you say the Beracha (blessing).
What's the reason for that? The Mishnah Berurah dissects this into two things, number one, and number two, he has to hold it and with the right hand. Why does he have to hold it at all? The reason you hold it is so that you have a Kavanah about what you are saying the Beracha for, which means that the Beracha is a general Beracha. Let's say it's an apple: you say Bore Peri Ha'etz (Who creates the fruit of the tree) on the apple. It's a general Beracha for all the fruits, but you have to have Kavanah that what you are saying the Beracha for is this apple. It's interesting, but it's not exclusive, because if it were exclusive, then you would have to say the Beracha on an orange, which sometimes happens. If it is exclusive for you, then you have to say Beracha again.
But it's exclusive enough for the Beracha, but inclusive for other things. Why with the right hand? He brings a Ta'am (reason): Mishum Chashivut, because it's more important. Even without going into Kabbalistic things, if your right hand is the one you usually use for things, then you do it. We see this concept all over Halacha (Jewish law). It's not only in this Halacha that you do it; it's everywhere.
Now, what happens if a person is a lefty? Does he use his right hand or not? You use the left hand because it's simple; we're talking about Chashivut here, so whatever you would give the Chashivut to—if you play tennis with the left hand, then you have to eat with the left hand. That's the Halacha; it's brought down in the Shulchan Aruch.
Now, if a person did not hold the fruit in his hand, does he have to say Beracha again? The Shulchan Aruch says you have to wait until they bring the fruit, or whatever you're saying the Beracha on, in front of you. If it was not in front of you, you just say Beracha, because they know that somebody is saying, “I'm making you a coffee.” You say... And then a person comes in; it doesn't work. If the coffee is in your presence, then it works. Of course, you're supposed to hold it, but if you didn't, it has to be there.
The Gemara asks about the famous case of drinking water from the river. You drink water from the river, but the water is not there. The water you're going to say the Beracha on is coming; it's not there yet. So how does that work? What are you going to say? You had Kavanah? So here too, I had Kavanah: the coffee is coming. In Starbucks, you paid for the coffee; it's coming, it's coming. There's no shortage of coffee. Would that work or not? It's a big safek (doubt). You know why? Because the reason why... Don't tell me it's because you had Kavanah, because we just said Kavanah doesn't work; it has to be in front of you.
The Mishnah Berurah says there's a 100% chance that the water will end up in front of you. That's why the Beracha works. Over here, it depends on the person. So let's go back to Starbucks. You order a Starbucks coffee, you paid for it, and they're going to give it to you. Yeah, but a couple of things could happen in the middle. For example, they bring you the coffee and it spills, or they make it fall, or they sneeze on your coffee while they're doing it. Hopefully they give you the wrong coffee. There are so many things that could happen that usually don't, but so many things could happen. It's not like Amat HaMayim (water channel). With Amat HaMayim, you have the Kavanah and something is coming, and it's 100%. So your Kavanah matches what is going to happen. But here, since somebody else is holding your cup until they give it to you, your Kavanah doesn't work. If somebody said the Beracha like this, they would have to say Beracha again. As long as they don't have the item in front of them, it doesn't work.