I think this is a great question that a lot of people can relate to. I think the question addresses a few big topics: What does it mean to be original? How does the creative process work? What are the legal implications of copying a song?

First, it's worth stating the obvious--that you're not the first person this has happened to. When writing ["Impressions,"](https://www.youtube.com/watch?v=-mZ54FJ6h-k) Coltrane copied [a section of a tune called "Pavanne"](https://www.youtube.com/watch?v=HRbslD5nz-8#t=1m14s) by Morton Gould. Then, Hank Mobley copied Coltrane when writing [Chain Reaction](https://www.youtube.com/watch?v=hJQuL0rw4h0). In Coltrane's case, this was probably subconscious. In Mobley's case, I would bet this started as a [contrafact](https://en.wikipedia.org/wiki/Contrafact) and was similar by design. Maybe Mobley was paying homage to Coltrane, or maybe he thought he could improve Impressions to the point of writing an altogether new song.

My take on this is that it's impossible to be perfectly original. There are a lot of things we should expect to repeat within a genre: chord changes, drum beats, baselines, chord voicings, and even small fragments of melodies and lyrics. Our musical ideas are based on what we have previously heard and played, and this is simply how the brain works: we rely on past examples when learning and creating. In his article entitled ["Inflexible Knowledge: The First Step to Expertise"](https://www.aft.org/periodical/american-educator/winter-2002/ask-cognitive-scientist#sthash.KQ872f3F.dpuf), UVA psychologist Daniel Willingham puts it this way: "the mind much prefers that new ideas be framed in concrete rather than abstract terms." In music, those concrete terms consist of chord changes, drum beats, baselines, and everything else I mentioned above. I see reuse as an integral part of the creative process.

That said, our creative products evolve and develop with practice and experience. As a musician spends more time playing and listening, her musical vocabulary grows. With time and experience, her creative process will produce increasingly more original and more unique work. In jazz, this same progression occurs in one's improvisational abilities and is usually encouraged by teachers. When I first started improvising, my teacher told me to pick a pianist and transcribe + learn an entire album of his solos. I chose Kenny Barron, and so at the beginning, every time I improvised I sounded like a **much** worse, unsophisticated version of Kenny Barron. As I transcribed more and more artists and practiced a range of different techniques, I built up a wider variety of licks, phrases, and rhythmic ideas from which to create a solo. This gave me more freedom, and I felt like I was being more creative, even though I was still using a very similar process as when I was just starting.

I don't mind this quality of musical creation, and I don't think it devalues the creative process. This is the same process (of reusing and recycling old ideas) that has produced many outstanding pieces of music. Given how the process works and evolves, I think one's expectations for originality should be commensurate with the level of experience. We set different expectations for beginners vs. experts when it comes to technique, skill, etc. I think originality/creativity of songwriting should receive the same treatment. So I see nothing wrong with a new guitarist writing a song--intentionally or unintentionally--that is the same chords and melody as MJLD but with different lyrics.

In my mind, the only prohibitive considerations are what the law does and doesn't allow. This is probably only relevant if you plan to publish your music or perform in public. The legal implications of copying a song vary from country to country and fall under the domain of copyright law. The copyright laws surrounding music are fascinating, and there are various rules/tests for determining infringement, but I think that particular topic doesn't fit within the music.SE site. That might be better suited for https://law.stackexchange.com.