The type of classes you are looking at and the type of student you are has a great deal do with if an college college course will be hard for you. These are important factors to remember when you are deciding if you will take an online course.
You must be if you are sooner to studying hard or are sooner to slacking. Self awareness is important in this decision. Do not try and fool yourself. There are other things to consider in deciding if a course you are considering would be difficult.
Take a hard look at the area you are considering. Some areas of study are going to be harder than others. However, of you are motivated and focused you can weather just about any challenge. You may choose something that seems above you like law or the medicine if you feel a great desire to succeed at these more challenging subjects.
Anyone who has taken some courses in college knows that not all classes are equal in difficulty. Classes in one's major area of study are usually full of detailed instruction on techniques. They also entail learning essential formulas and facts. Other have been termed fillers.
Other courses are more for personal general interest and are sometimes called fillers. They may be interesting but are not as challenging. Filler courses will be the easier of the two types to take online.
Traditional college courses include interaction with a professor that is just not part of the design of online courses. Some students just have a difficulty grasping this concept and can not handle it, while others excel in this setting.
If you feel you need in person instruction, then online courses probably are not for you. They do not have traditional office hours and time after class to work with you.
In considering taking an online course, make sure you have done some research before taking the plunge.