Can you learn Spanish fast on your own?
Of course you can. Thousands and thousands of people have done it before you and there is really no legitimate reason that you could not do it. Learning Spanish fast on your own is not that hard if you know what you are doing.
There is actually only one real danger when you want to learn Spanish on your own. You must not try to be too smart. What do I mean by this? You are a smart person, probably an expert in your field of expertise and you know what to do in cases related to your occupation. But you are probably not an expert in teaching foreign languages, are you? So why not leave the guidance to the people who are experts in teaching Spanish and use their experience, advice and knowledge to your advantage?
What I’m trying to say here is this: you most definitely can learn Spanish fast on your own if you follow a laid-out path for learning Spanish by a quality Spanish learning course, put together by experts in teaching Spanish language.
Save yourself a lot of time, effort and money and find a really good Spanish learning course that will suite your needs and then follow it. Don’t try to be smarter than the people who have years and years of hands-on experience with teaching Spanish and guiding learners through the process of Spanish learning to minimize the effort and time needed and maximize the results and learn Spanish as fast as possible.