Consider doing your addition or subtraction on a number line. To save space, I'll use the example of 3 - 5, rather than the original. On a number line, addition is done by moving to the right and subtraction is done bymoving to the left. So, if you wanted to add 1 + 2, you'd start at 1 and move 2 spaces right. Similarly, to subtract 3 - 5, you start at three and move 5 spaces left:

-4...-3...-2...-1....0....1....2....3....4....5
....................................X (start here)
...............................X (move 1 space left ...)
..........................X (move 2 spaces left ...)
.....................X (move 3 spaces left ...)
................X (move 4 spaces left ...)
...........X (move 5 spaces left ... and you're done!)

As you can see, you're now at -2, not 2. Try this with the original operation of 14 - 27, and you'll find yourself ending up at -13, not 13.

And I've just noticed that I'm typing this in a monospace font, but it will be posted in a proportional font. If you have trouble reading my diagram above, copy it into a word processor and format it into a monospace font such as Courier.