As an avid photographer, I have over time experienced and owned many different camera brands - Minolta, Pentax, Olympus, FujiFilm, and Nikon to name a few. In my early days, I used three basic lenses, a wide-angle 24mm, a 50mm, and a medium telephoto 200mm, back then film cameras were simple, cheap and mostly manual in their operation. As technology advanced film cameras merged with the age of electronics and we found ourselves in the world of digital cameras. Many name brand cameras started to move their Film based systems to the digital format and the competition was and still is fierce. In the early days of DSLRs, camera companies were in a race for more megapixels, those who had the most wore the crown. Companies knew that in order to persuade Film users to move to the digital age the images needed to exceed the quality of a Film print, and that was possible with more megapixels.
Fast forward to today. The remaining camera companies are all vying for your attention and money. The competition between camera manufacturers have for the most part split into various camps - the Mirrorless full frame camp, The Mirrorless Crop Sensor camp, and Micro Four Thirds camp, plus the DSLRs that are common and still widely available for those who do not wish to move to Mirrorless as of yet. Prosumer cameras and lenses that are currently available are in most cases not cheap and if you make a choice to buy and use crop sensor systems or Micro Four Thirds or even Full Frame you shell out a considerable investment, keeping in mind newer camera models are being released with the hopes that you upgrade, which eventually you do. Over time you acquire a line of Brand X lenses and a couple of camera bodies.
At some point, you get an itch to try a different camera brand, and you decide to give it a try. Along with buying the new camera, you also buy a lens or two, and this investment will be at the expense of funding your "normal" system. So, you forgo that dream lens you have been saving for and drop those funds on brand X camera and lens. Here is what I have learned and have decided to do to focus my time, attention, and funds on one single brand and why you should do the same. Let me be clear, it is perfectly fine to buy gear for your system as long as it can be used with your main system - like a Nissan Flash for your Sony or Nikon - that is not money wasted because it supports your system. The issue arises when you have multiple camera lenses and bodies that are only compatible with their brand, leaving you with redundant equipment such as Brand X with a 24-70 and Brand Y with a 24-70.
Don't Get Emotionally Attached: It is perfectly fine to make a switch from camera brands if the switch better supports your photography needs. When making a switch you need to do a lot of soul-searching and research. Do not allow other peoples emotions influence you on a system - stick to the facts, what is it you need? Does the brand you are considering have the lenses that support your needs and are a financially viable solution? Do the third party manufactures support the camera system that you are considering (Flash, Lens, etc)? Once you release your emotions and look at the options with a clear mind and conscience it will become more apparent in which direction you should move but don't move just yet, take a few weeks to study your current inventory and assess what it will take to replace those items you use most often first: make a list in priority order.
Shed the Excess Baggage: Having multiple camera systems is a distraction and a financial burden. Why are you investing in multiple systems rather than expanding your current system? If your current camera system is not meeting your goals then consider making a brand switch by all means. To maximize your photography consider selling your redundant non-used gear. We all have a few lenses or camera bodies we hold on to for sentimental reasons and never really use them - they take up space.
Time Changes Everything: Before Nikon released the Z series of their full frame mirrorless cameras I purchased three Fujifilm mirrorless cameras for the experience and feel of using a mirrorless camera to help me decide if a mirrorless could replace my DSLRs. Now that Nikon Z7 and Z6 have entered the marketplace and I now use a Nikon Z7 - I don't need the Fujifilm XT-2 or XT-3 mirrorless cameras as Nikon now fills that mirrorless niche. Keeping the Fujifilm Cameras and Lens is not a wise use of funds as I would rather invest in the new Nikon Mirrorless systems going forward rather than split resources between the two camera lines. Having said that, I sold my XT-2 and will be selling the remainder of the Fujifilm gear - it was nice using the Fujifilm XT-2/3 but alas I say bye to Fujifilm and hello Nikon Mirrorless.
In addition to selling the Fujifilm cameras, I sold the awesome Nikon D500 with Battery grip as well. When all is said and done I will retain a Nikon D850, Nikon Z7, and a Nikon Z6 and thus be a one camera Manufacture photographer once again - Nikon.