In this circumstance…yes. While “a once in a lifetime” opportunity comes around…well, once in a lifetime, it would be unprofessional to bail so early into your tenure with your organization.

No reasonable employer expects its employees to stay forever (anymore). But there is an expectation that an employee will be committed to stay for a “reasonable” period of time once s/he accepts an offer of employment. So what is reasonable anyway? The minimum length of time to stay in a position – which the market and employers generally accept as reasonable, is 2 years (which has decreased significantly over the past 15-20 years). Less than two years can reach reasonable status in some circumstances, but anything less than a year can leave a negative impression on you, your character and the size of your wings. Of course, there are always exceptions, but not many that leave a boss giving a lawyer a warm and fuzzy bon voyage.

Does this situation fall into one of those special exceptions? No. You mention that this newly presented position is a once in a lifetime opportunity. But you don’t have enough information to know how compelling it actually is or is not.  A conversation or two with a recruiter does not suffice. Even if it is fabulous, this fact isn’t compelling enough to outweigh the strength of your new commitment to your current employer. In addition, you like your new job. So what is driving you to consider leaving a job you already enjoy? This grass is greener mentality is flawed and almost always results in a compromised career and reputation.

In your situation, you have given your employer a commitment. Your word. In return, your colleagues have invested time and their own commitment to you as a new team member. The organization has also bypassed other candidates in favor of choosing you. Part of that decision involved an expectation and reliance that you would not immediately leave for the next best thing that came your way. While you are not legally obligated to stay, a strong professional value system would dictate that you do.

Seemingly great job opportunities are tempting to explore further. And in most circumstances, it would behoove you to take a closer look.  But when tenure with your current employer is only a few months, you’re better off looking the other way. So stay put and focus on succeeding in your new role. There will be more once in a lifetime opportunities to come. I promise.