Photoshop's lasso tool can be used to select the desired area at will, and when you choose, you can decide which parts to select by dragging the mouse. Often, when used, we often make a partial enlargement of the view before making a selection, so that we can create more precise selections. (Note: This article refers to the "lasso tool" is generally speaking, including "polygonal lasso tool" and "magnetic lasso tool." )
Many novice Photoshop friends are using the lasso tool, often plagued by problems like this--when you zoom in on the view, drag the selection with the Lasso tool, and when you drag to the edge of the window, you want to continue the selection, you can always move the mouse pointer outside the window, and the view will move far away. Instead of using the scroll bar to move the view.
As shown in Figure 1, the mouse has been dragged to the edge of the window.
Figure 1
As you move the pointer down a bit, the resulting view moves a great chunk of distance, and the selected selection is not visible, as shown in Figure 2.